A variety of internal and external sensors exist to monitor brain parameters. Electroencephalography (EEG), for example, utilizes a plurality of external electrical sensors, attached to the scalp, to monitor electrical activity in the brain. The EEG can be used clinically to detect anomalies (such as epilepsy), diagnose sleep issues, and determine the severity of brain injury after an accident, among other things. In the event of serious brain injury, for example, the EEG can be used to differentiate between coma, vegetative state, and complete brain death.
In the event of brain injury and/or infection, for example, the brain has a tendency to swell. As the brain swells, it compresses the surrounding intracranial fluid, increasing the pressure on the brain. Unfortunately, this pressure can damage the brain physically and can reduce blood flow to the brain causing oxygen deprivation and possible death to brain tissue. This secondary type of brain injury is often more extensive than the original injury to the brain (e.g., from a head trauma).
After injury or infection, therefore, it can be beneficial to monitor intracranial pressure (ICP) for several hours or days to ensure the brain edema subsides and to prevent further injury. This overpressure situation can often be reduced, or eliminated, for example, simply by draining a portion of the cerebral fluid out of the skull through a burr hole. In less severe cases, brain swelling and brain tissue oxygen demand can be reduced by externally cooling the brain. This can enable the swelling to subside naturally, which may obviate the need for a burr hole.
In either case, an intracranial pressure sensor inserted directly into the skull can provide accurate ICP readings. These sensors can be simple capillary type sensors connected to an external gauge, for example, or can be electronic gauges based on strain gauge, or other technologies. A problem with conventional mechanical and electronic gauges, however, is that they generally require an external connection to be read. A capillary type gauge, for example, must be connected to a dial, or other apparatus, to read the ICP. Electronic gauges, on the other hand, can require wires, or other means, to be attached to the patient to enable monitoring. The attached wires can increase patient discomfort by pulling on the wound site and increasing infection and can also cause accidents resulting from entanglement of the wires, among other things.
In addition, many patients that receive invasive ICP monitoring have limited consciousness and, as a result, may have limited, or no, mobility. As a result, they generally must be, for example, handled, turned, and moved by caregivers to facilitate bathing and sheet changes, among other things. During handling, the cables and wires from conventional sensors can be accidentally pulled or broken by the caregivers. This, in turn, can result in sensors breaking or pulling out of the brain tissue and a loss of functionality. When this happens, a new sensor must be placed in a new location resulting in an additional procedure, additional disruption of brain tissue, and additional cost to the hospital.
To address these issues, wireless sensors have been developed. Unfortunately, these too suffer from a number of drawbacks. One type of wireless sensor, for example, as disclosed in U.S. Patent Pub. No. 2010/0030103, includes a sensor, an external coil, or antenna, for communication. This type of sensor possesses no internal memory or other storage. To collect data from the sensor, therefore, an interrogator must be placed in close proximity to the sensor at all times. This “semi-wired” configuration, in which the sensor must be read externally with a reader, substantially defeats the purpose of the wireless component of the sensor.
In addition, conventional sensors have electronic components that are permanently, or semi-permanently, implanted in, or attached to, the patient's body. In this configuration, the many components of the sensor, which can include, for example, antennas, batteries, silicon chips, RFID chips, and other electronic components, generally cannot be removed without removing the entire sensor. Depending on the application, this may require involved procedures, even including surgical intervention. These components can, at a minimum, interfere with ongoing testing such as X-rays, MRIs, and other imaging. At worst, these components can actually injure the patient. Batteries and other metallic objects, for example, can actually physically move or be heated to the point of explosion by magnetic resonance imaging (MRI). In addition, many components may be rendered inoperable by x-rays and other radiation.
What is needed, therefore, is a wireless, modular sensor capable of reading one or more bodily functions. The sensor should be modular, such that some, or all, of its components can be easily removed for testing and then reinstalled. The sensor should include a secure mounting solution to enable removal and installation of these components with little or no discomfort to the patient. It is to such a system that examples of the present invention are primarily directed.